Roundabout evaluation and design: a site selection procedure

R. F. Benekohal, Varun Atluri

Research output: Book/Report/Conference proceedingTechnical report


This study surveyed IDOT staff about roundabouts, evaluated two popular roundabout software programs (aaSIDRA and RODEL), developed a multi-criteria site selection procedure, and used it to identify 10 potential intersections in Illinois that may reduce fatalities and severe injuries by using a roundabout. IDOT jurisdiction includes three roundabouts built or under construction and four roundabouts in planning stages. One third of IDOT districts were familiar with the RODEL and aaSIDRA, but they did not have working knowledge of the software. Some districts were concerned about proper roundabout usage by unfamiliar, younger, or elderly drivers. For the same traffic conditions, aaSIDRA yielded higher delay than RODEL for most of the reasonable volume combinations. Capacity values from RODEL are very similar to FHWA’s 2000 Guide and both are higher than the new NCHRP 572 model, but aaSIDRA’s capacity curves are similar to that of NCHRP 572. This study used aaSIDRA for developing the proposed site selection procedure. A multi-criteria site selection procedure was developed and its application is presented. The factors considered in the site selection process included crash history, intersection delay (LOS), roundabout capacity, distribution of traffic volume among approaches, location of intersection, and input from “local” engineers. The site selection process was used to identify the top 10 potential roundabout locations in Illinois. Further modification to this procedure is needed to cover other types of roads (multi lane) and traffic conditions. It is recommended that, for the time being, IDOT follow the FHWA Roundabout Guide (2000) in conjunction with the findings of recently published NHCRP Report 572 as a guideline for the design of roundabouts. The upcoming FHWA Roundabout Guide and a new roundabout chapter in the 2010 Highway Capacity Manual will include significantly new information that could be used in developing a roundabout design guide for IDOT.
Original languageEnglish (US)
Place of PublicationUrbana, Ill
PublisherIllinois Center for Transportation
StatePublished - 2009

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